Biocompatible silicones have been used as encapsulation layers for decades but it is known that most silicones tend to have a rather large water vapor transmission rate (WVTR) due to their porous structure. One way to reduce the WVTR by adding another parylene-C coating on silicone is reported to seal the silicone layer and have very good adhesion to it (see, S. Sawano et al., Digest Tech. Papers MEMS'08 Conference, Tucson, USA, Jan. 13-17, 2008, pp. 419-422). However, the parylene-C coated bio-compatible silicone layer tends to be thick and can lose its elastic flexibility.
On the other hand, parylene-C has been extensively used in biomedical devices and interfaces as a structural material or a conformal and bio-compatible coating (see, J. H. Chang, R. Huang, Y. C. Tai, Digest Tech. Papers Transducers '11 Conference, Peking, Jun. 5-9, 2011, pp. 378-381). It has also become a packaging material because of its many favorable properties (see, J. H. Chang, D. Kang, Y. C. Tai, Digest Tech. Papers MEMS'12 Conference, Paris, Jan. 29-Feb. 2, 2012, pp. 353-356). The water permeability and the chemical stability of parylene-C have also been studied (see, Y. Hu et al., Journal of Applied Polymer Science, vol. 81, pp. 1624-1633, 2000; W. Li et al., ECS Transactions, vol. 11, pp. 1-6, 2008), and the results show that parylene-C is a very good bioinert insulator and parylene-C protected electrodes can survive a sufficiently long time with metals sandwiched by 9.2 μm parylene-C on each side.
One of the biggest challenges that a prosthetic implant has to overcome is the reliable packaging of integrated circuit (IC) chips so that bio-devices can withstand corrosive body fluids. What is needed in the art is a complete wireless retinal implant with high density multi-channel IC chips, discrete components (caps, inductors, and oscillators), and coils (power and data coils) packaged with a high-density stimulating electrode array. Appropriate packaging of the retinal implant in a mammalian body to achieve a long lifetime is also needed. The present invention satisfies these and other needs.